Differential induction of chitinase and 1,3-beta-glucanase gene expression in tomato by Cladosporium fulvum and its race-specific elicitors

Accumulation of pathogenesis-related proteins is an important feature of plant defence responses upon infection by pathogens. In the interaction between Cladosporium fulvum and tomato, resistance against the fungus correlates with early induction of transcription of genes encoding apoplastic chitinase and 1,3-beta-glucanase and the accumulation of these proteins in inoculated tomato leaves. For vacuolar, basic isoforms of chitinase and 1,3-beta-glucanase, however, early gene transcript accumulation was observed in both incompatible and compatible interactions. Here we report on the tissue-specific expression of genes encoding these hydrolytic enzymes as studied by means of in situ hybridization. Only temporal differences in gene transcript accumulation were observed for each isoform studied. Expression of the acidic chitinase gene was observed primarily near leaf vascular tissue. Expression of the basic chitinase and the basic and acidic 1,3-beta-glucanase genes was less confined to particular tissues. No preferential accumulation of gene transcripts in tissue near penetrating hyphae was observed in compatible or incompatible interactions. Injection of purified race-specific elicitors, AVR4 and AVR9, in tomato genotypes Cf4 and Cf9, respectively, induced primarily differential expression of acidic chitinase and acidic 1,3-beta-glucanase. The induction, observed most abundantly in resistant genotypes, correlates well with the difference in gene expression previously observed in time course experiments of compatible and C. fulvum-tomato interactions. (C) 1996 Academic Press Limited